1. Field of the Invention
The present invention relates generally to a lens barrel and, more particularly, to a lens barrel capable of preventing a backlash or play between movement cam mechanisms for moving lens units.
2. Related Background Art
This type of lens barrel has hitherto incorporated a plurality of lens units each performing a different operation, e.g., a second lens unit L2 and a third lens unit L3 that are illustrated in FIGS. 1 and 2. The lens units L2, L3 are individually held by unit lens drums 5, 6 fitted to a fixed drum 1 of the lens barrel. The individual unit lens drums 5, 6 are provided with pins 5a, 6a which are fitted in grooves 4c, 4b, whereby the movement cam mechanism is constructed.
Accordingly, the construction is such that referring to, e.g., FIG. 1, when zoomed by rotating a cam ring 3, with a work of the above movement cam mechanism, the respective lens units L2, L3 are moved along an optical axis A as illustrated in FIG. 2, and a variety of functions are performed. In this case, providing the individual pins 5a, 6a with smooth shifts within the respective grooves 4c, 4b involves forming predetermined play air gaps (slide allowances) between the pins 5a, 6a and the grooves 4c, 4b.
If those components remain as they are, however, this may cause a "backlash" of the movement cam mechanism members, and, therefore, a biasing member 10 such as a helical spring is provided between the respective lens units L2 and L3 in this type of lens barrel 200. This biasing member 10 biases the lens units L2, L3 respectively in the optical-axis direction A, with the result that the pins 5a, 6a are pushed against one sides of the grooves 4c, 4b. A backlash in the movement cam mechanism is thereby prevented.
In the above conventional lens barrel 200, however, an interval between the lens units L2 and L3 varies, and, because of variations in value of the biasing force of the biasing member 10 acting therebetween, there arises such a problem that an inconstant cam operation is done when performing a zooming or focusing process.